The long-term objective of the project is to elucidate the molecular basis for herb-drug interactions, and to develop molecular-based technologies to predict such interactions. The major objective of this project is to reveal molecular details involving the activation of the pregnane X receptor (PXR) by Chinese herbal extracts and model compounds hyperforin and guggulsterone. The model compounds represent the most used herbal supplements, and are shown to activate PXR. Activation of this receptor markedly induces the expression of drug-metabolizing enzymes, resulting in severe herb-drug interactions. PXR is a member of the nuclear receptor superfamily, and recruits very same coactivators as other nuclear receptors. Interestingly, hyperforin is more potent toward human PXR, whereas guggulsterone is more potent toward rodent PXRs. The goals of this project are: (1) to determine the structural basis for the species-preferable activation;(2) to determine whether Chinese herbal extracts, known to induce drug-metabolizing enzymes, activate PXR;(3) to determine whether depletion of coactivators reduces hyperforin-mediated activation of PXR;and (4) to provide the applicant with a much-needed exercise on high-end molecular techniques.